#include "cache.h"
#include "builtin.h"
#include "parse-options.h"
#include "refs.h"
#include "commit.h"
#include "tree.h"
#include "tree-walk.h"
#include "unpack-trees.h"
#include "dir.h"
#include "run-command.h"
#include "merge-recursive.h"
#include "branch.h"
#include "diff.h"
#include "revision.h"
#include "remote.h"

static const char * const checkout_usage[] = {
        "git checkout [options] <branch>",
        "git checkout [options] [<branch>] -- <file>...",
        NULL,
};

static int post_checkout_hook(struct commit *old, struct commit *new,
                              int changed)
{
        struct child_process proc;
        const char *name = git_path("hooks/post-checkout");
        const char *argv[5];

        if (access(name, X_OK) < 0)
                return 0;

        memset(&proc, 0, sizeof(proc));
        argv[0] = name;
        argv[1] = xstrdup(sha1_to_hex(old->object.sha1));
        argv[2] = xstrdup(sha1_to_hex(new->object.sha1));
        argv[3] = changed ? "1" : "0";
        argv[4] = NULL;
        proc.argv = argv;
        proc.no_stdin = 1;
        proc.stdout_to_stderr = 1;
        return run_command(&proc);
}

static int update_some(const unsigned char *sha1, const char *base, int baselen,
                       const char *pathname, unsigned mode, int stage)
{
        int len;
        struct cache_entry *ce;

        if (S_ISGITLINK(mode))
                return 0;

        if (S_ISDIR(mode))
                return READ_TREE_RECURSIVE;

        len = baselen + strlen(pathname);
        ce = xcalloc(1, cache_entry_size(len));
        hashcpy(ce->sha1, sha1);
        memcpy(ce->name, base, baselen);
        memcpy(ce->name + baselen, pathname, len - baselen);
        ce->ce_flags = create_ce_flags(len, 0);
        ce->ce_mode = create_ce_mode(mode);
        add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
        return 0;
}

static int read_tree_some(struct tree *tree, const char **pathspec)
{
        read_tree_recursive(tree, "", 0, 0, pathspec, update_some);

        /* update the index with the given tree's info
         * for all args, expanding wildcards, and exit
         * with any non-zero return code.
         */
        return 0;
}

static int checkout_paths(struct tree *source_tree, const char **pathspec)
{
        int pos;
        struct checkout state;
        static char *ps_matched;
        unsigned char rev[20];
        int flag;
        struct commit *head;

        int newfd;
        struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));

        newfd = hold_locked_index(lock_file, 1);
        read_cache();

        if (source_tree)
                read_tree_some(source_tree, pathspec);

        for (pos = 0; pathspec[pos]; pos++)
                ;
        ps_matched = xcalloc(1, pos);

        for (pos = 0; pos < active_nr; pos++) {
                struct cache_entry *ce = active_cache[pos];
                pathspec_match(pathspec, ps_matched, ce->name, 0);
        }

        if (report_path_error(ps_matched, pathspec, 0))
                return 1;

        memset(&state, 0, sizeof(state));
        state.force = 1;
        state.refresh_cache = 1;
        for (pos = 0; pos < active_nr; pos++) {
                struct cache_entry *ce = active_cache[pos];
                if (pathspec_match(pathspec, NULL, ce->name, 0)) {
                        checkout_entry(ce, &state, NULL);
                }
        }

        if (write_cache(newfd, active_cache, active_nr) ||
            commit_locked_index(lock_file))
                die("unable to write new index file");

        resolve_ref("HEAD", rev, 0, &flag);
        head = lookup_commit_reference_gently(rev, 1);

        return post_checkout_hook(head, head, 0);
}

static void show_local_changes(struct object *head)
{
        struct rev_info rev;
        /* I think we want full paths, even if we're in a subdirectory. */
        init_revisions(&rev, NULL);
        rev.abbrev = 0;
        rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
        add_pending_object(&rev, head, NULL);
        run_diff_index(&rev, 0);
}

static void describe_detached_head(char *msg, struct commit *commit)
{
        struct strbuf sb;
        strbuf_init(&sb, 0);
        parse_commit(commit);
        pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, 0, "", "", 0, 0);
        fprintf(stderr, "%s %s... %s\n", msg,
                find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
        strbuf_release(&sb);
}

static int reset_to_new(struct tree *tree, int quiet)
{
        struct unpack_trees_options opts;
        struct tree_desc tree_desc;
        memset(&opts, 0, sizeof(opts));
        opts.head_idx = -1;
        opts.update = 1;
        opts.reset = 1;
        opts.merge = 1;
        opts.fn = oneway_merge;
        opts.verbose_update = !quiet;
        parse_tree(tree);
        init_tree_desc(&tree_desc, tree->buffer, tree->size);
        if (unpack_trees(1, &tree_desc, &opts))
                return 128;
        return 0;
}

static void reset_clean_to_new(struct tree *tree, int quiet)
{
        struct unpack_trees_options opts;
        struct tree_desc tree_desc;
        memset(&opts, 0, sizeof(opts));
        opts.head_idx = -1;
        opts.skip_unmerged = 1;
        opts.reset = 1;
        opts.merge = 1;
        opts.fn = oneway_merge;
        opts.verbose_update = !quiet;
        parse_tree(tree);
        init_tree_desc(&tree_desc, tree->buffer, tree->size);
        if (unpack_trees(1, &tree_desc, &opts))
                exit(128);
}

struct checkout_opts {
        int quiet;
        int merge;
        int force;

        char *new_branch;
        int new_branch_log;
        enum branch_track track;
};

struct branch_info {
        const char *name; /* The short name used */
        const char *path; /* The full name of a real branch */
        struct commit *commit; /* The named commit */
};

static void setup_branch_path(struct branch_info *branch)
{
        struct strbuf buf;
        strbuf_init(&buf, 0);
        strbuf_addstr(&buf, "refs/heads/");
        strbuf_addstr(&buf, branch->name);
        branch->path = strbuf_detach(&buf, NULL);
}

static int merge_working_tree(struct checkout_opts *opts,
                              struct branch_info *old, struct branch_info *new)
{
        int ret;
        struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
        int newfd = hold_locked_index(lock_file, 1);
        read_cache();

        if (opts->force) {
                ret = reset_to_new(new->commit->tree, opts->quiet);
                if (ret)
                        return ret;
        } else {
                struct tree_desc trees[2];
                struct tree *tree;
                struct unpack_trees_options topts;
                memset(&topts, 0, sizeof(topts));
                topts.head_idx = -1;

                refresh_cache(REFRESH_QUIET);

                if (unmerged_cache()) {
                        error("you need to resolve your current index first");
                        return 1;
                }

                /* 2-way merge to the new branch */
                topts.update = 1;
                topts.merge = 1;
                topts.gently = opts->merge;
                topts.verbose_update = !opts->quiet;
                topts.fn = twoway_merge;
                topts.dir = xcalloc(1, sizeof(*topts.dir));
                topts.dir->show_ignored = 1;
                topts.dir->exclude_per_dir = ".gitignore";
                tree = parse_tree_indirect(old->commit->object.sha1);
                init_tree_desc(&trees[0], tree->buffer, tree->size);
                tree = parse_tree_indirect(new->commit->object.sha1);
                init_tree_desc(&trees[1], tree->buffer, tree->size);

                if (unpack_trees(2, trees, &topts)) {
                        /*
                         * Unpack couldn't do a trivial merge; either
                         * give up or do a real merge, depending on
                         * whether the merge flag was used.
                         */
                        struct tree *result;
                        struct tree *work;
                        if (!opts->merge)
                                return 1;
                        parse_commit(old->commit);

                        /* Do more real merge */

                        /*
                         * We update the index fully, then write the
                         * tree from the index, then merge the new
                         * branch with the current tree, with the old
                         * branch as the base. Then we reset the index
                         * (but not the working tree) to the new
                         * branch, leaving the working tree as the
                         * merged version, but skipping unmerged
                         * entries in the index.
                         */

                        add_files_to_cache(0, NULL, NULL);
                        work = write_tree_from_memory();

                        ret = reset_to_new(new->commit->tree, opts->quiet);
                        if (ret)
                                return ret;
                        merge_trees(new->commit->tree, work, old->commit->tree,
                                    new->name, "local", &result);
                        reset_clean_to_new(new->commit->tree, opts->quiet);
                }
        }

        if (write_cache(newfd, active_cache, active_nr) ||
            commit_locked_index(lock_file))
                die("unable to write new index file");

        if (!opts->force)
                show_local_changes(&new->commit->object);

        return 0;
}

static void report_tracking(struct branch_info *new, struct checkout_opts *opts)
{
        /*
         * We have switched to a new branch; is it building on
         * top of another branch, and if so does that other branch
         * have changes we do not have yet?
         */
        char *base;
        unsigned char sha1[20];
        struct commit *ours, *theirs;
        char symmetric[84];
        struct rev_info revs;
        const char *rev_argv[10];
        int rev_argc;
        int num_ours, num_theirs;
        const char *remote_msg;
        struct branch *branch = branch_get(new->name);

        /*
         * Nothing to report unless we are marked to build on top of
         * somebody else.
         */
        if (!branch || !branch->merge || !branch->merge[0] || !branch->merge[0]->dst)
                return;

        /*
         * If what we used to build on no longer exists, there is
         * nothing to report.
         */
        base = branch->merge[0]->dst;
        if (!resolve_ref(base, sha1, 1, NULL))
                return;

        theirs = lookup_commit(sha1);
        ours = new->commit;
        if (!hashcmp(sha1, ours->object.sha1))
                return; /* we are the same */

        /* Run "rev-list --left-right ours...theirs" internally... */
        rev_argc = 0;
        rev_argv[rev_argc++] = NULL;
        rev_argv[rev_argc++] = "--left-right";
        rev_argv[rev_argc++] = symmetric;
        rev_argv[rev_argc++] = "--";
        rev_argv[rev_argc] = NULL;

        strcpy(symmetric, sha1_to_hex(ours->object.sha1));
        strcpy(symmetric + 40, "...");
        strcpy(symmetric + 43, sha1_to_hex(theirs->object.sha1));

        init_revisions(&revs, NULL);
        setup_revisions(rev_argc, rev_argv, &revs, NULL);
        prepare_revision_walk(&revs);

        /* ... and count the commits on each side. */
        num_ours = 0;
        num_theirs = 0;
        while (1) {
                struct commit *c = get_revision(&revs);
                if (!c)
                        break;
                if (c->object.flags & SYMMETRIC_LEFT)
                        num_ours++;
                else
                        num_theirs++;
        }

        if (!prefixcmp(base, "refs/remotes/")) {
                remote_msg = " remote";
                base += strlen("refs/remotes/");
        } else {
                remote_msg = "";
        }

        if (!num_theirs)
                printf("Your branch is ahead of the tracked%s branch '%s' "
                       "by %d commit%s.\n",
                       remote_msg, base,
                       num_ours, (num_ours == 1) ? "" : "s");
        else if (!num_ours)
                printf("Your branch is behind the tracked%s branch '%s' "
                       "by %d commit%s,\n"
                       "and can be fast-forwarded.\n",
                       remote_msg, base,
                       num_theirs, (num_theirs == 1) ? "" : "s");
        else
                printf("Your branch and the tracked%s branch '%s' "
                       "have diverged,\nand respectively "
                       "have %d and %d different commit(s) each.\n",
                       remote_msg, base,
                       num_ours, num_theirs);
}

static void update_refs_for_switch(struct checkout_opts *opts,
                                   struct branch_info *old,
                                   struct branch_info *new)
{
        struct strbuf msg;
        const char *old_desc;
        if (opts->new_branch) {
                create_branch(old->name, opts->new_branch, new->name, 0,
                              opts->new_branch_log, opts->track);
                new->name = opts->new_branch;
                setup_branch_path(new);
        }

        strbuf_init(&msg, 0);
        old_desc = old->name;
        if (!old_desc)
                old_desc = sha1_to_hex(old->commit->object.sha1);
        strbuf_addf(&msg, "checkout: moving from %s to %s",
                    old_desc, new->name);

        if (new->path) {
                create_symref("HEAD", new->path, msg.buf);
                if (!opts->quiet) {
                        if (old->path && !strcmp(new->path, old->path))
                                fprintf(stderr, "Already on \"%s\"\n",
                                        new->name);
                        else
                                fprintf(stderr, "Switched to%s branch \"%s\"\n",
                                        opts->new_branch ? " a new" : "",
                                        new->name);
                }
        } else if (strcmp(new->name, "HEAD")) {
                update_ref(msg.buf, "HEAD", new->commit->object.sha1, NULL,
                           REF_NODEREF, DIE_ON_ERR);
                if (!opts->quiet) {
                        if (old->path)
                                fprintf(stderr, "Note: moving to \"%s\" which isn't a local branch\nIf you want to create a new branch from this checkout, you may do so\n(now or later) by using -b with the checkout command again. Example:\n  git checkout -b <new_branch_name>\n", new->name);
                        describe_detached_head("HEAD is now at", new->commit);
                }
        }
        remove_branch_state();
        strbuf_release(&msg);
        if (!opts->quiet && (new->path || !strcmp(new->name, "HEAD")))
                report_tracking(new, opts);
}

static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
{
        int ret = 0;
        struct branch_info old;
        unsigned char rev[20];
        int flag;
        memset(&old, 0, sizeof(old));
        old.path = resolve_ref("HEAD", rev, 0, &flag);
        old.commit = lookup_commit_reference_gently(rev, 1);
        if (!(flag & REF_ISSYMREF))
                old.path = NULL;

        if (old.path && !prefixcmp(old.path, "refs/heads/"))
                old.name = old.path + strlen("refs/heads/");

        if (!new->name) {
                new->name = "HEAD";
                new->commit = old.commit;
                if (!new->commit)
                        die("You are on a branch yet to be born");
                parse_commit(new->commit);
        }

        /*
         * If the new thing isn't a branch and isn't HEAD and we're
         * not starting a new branch, and we want messages, and we
         * weren't on a branch, and we're moving to a new commit,
         * describe the old commit.
         */
        if (!new->path && strcmp(new->name, "HEAD") && !opts->new_branch &&
            !opts->quiet && !old.path && new->commit != old.commit)
                describe_detached_head("Previous HEAD position was", old.commit);

        if (!old.commit) {
                if (!opts->quiet) {
                        fprintf(stderr, "warning: You appear to be on a branch yet to be born.\n");
                        fprintf(stderr, "warning: Forcing checkout of %s.\n", new->name);
                }
                opts->force = 1;
        }

        ret = merge_working_tree(opts, &old, new);
        if (ret)
                return ret;

        update_refs_for_switch(opts, &old, new);

        return post_checkout_hook(old.commit, new->commit, 1);
}

int cmd_checkout(int argc, const char **argv, const char *prefix)
{
        struct checkout_opts opts;
        unsigned char rev[20];
        const char *arg;
        struct branch_info new;
        struct tree *source_tree = NULL;
        struct option options[] = {
                OPT__QUIET(&opts.quiet),
                OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
                OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
                OPT_SET_INT( 0 , "track",  &opts.track, "track",
                        BRANCH_TRACK_EXPLICIT),
                OPT_BOOLEAN('f', NULL, &opts.force, "force"),
                OPT_BOOLEAN('m', NULL, &opts.merge, "merge"),
                OPT_END(),
        };

        memset(&opts, 0, sizeof(opts));
        memset(&new, 0, sizeof(new));

        git_config(git_default_config);

        opts.track = git_branch_track;

        argc = parse_options(argc, argv, options, checkout_usage, 0);
        if (argc) {
                arg = argv[0];
                if (get_sha1(arg, rev))
                        ;
                else if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
                        new.name = arg;
                        setup_branch_path(&new);
                        if (resolve_ref(new.path, rev, 1, NULL))
                                new.commit = lookup_commit_reference(rev);
                        else
                                new.path = NULL;
                        parse_commit(new.commit);
                        source_tree = new.commit->tree;
                        argv++;
                        argc--;
                } else if ((source_tree = parse_tree_indirect(rev))) {
                        argv++;
                        argc--;
                }
        }

        if (argc && !strcmp(argv[0], "--")) {
                argv++;
                argc--;
        }

        if (!opts.new_branch && (opts.track != git_branch_track))
                die("git checkout: --track and --no-track require -b");

        if (opts.force && opts.merge)
                die("git checkout: -f and -m are incompatible");

        if (argc) {
                const char **pathspec = get_pathspec(prefix, argv);

                if (!pathspec)
                        die("invalid path specification");

                /* Checkout paths */
                if (opts.new_branch || opts.force || opts.merge) {
                        if (argc == 1) {
                                die("git checkout: updating paths is incompatible with switching branches/forcing\nDid you intend to checkout '%s' which can not be resolved as commit?", argv[0]);
                        } else {
                                die("git checkout: updating paths is incompatible with switching branches/forcing");
                        }
                }

                return checkout_paths(source_tree, pathspec);
        }

        if (new.name && !new.commit) {
                die("Cannot switch branch to a non-commit.");
        }

        return switch_branches(&opts, &new);
}