#include "cache.h"
#include "run-command.h"
#include "sigchain.h"

#ifndef DEFAULT_PAGER
#define DEFAULT_PAGER "less"
#endif

static struct child_process pager_process = CHILD_PROCESS_INIT;
static const char *pager_program;

static void wait_for_pager(int in_signal)
{
        if (!in_signal) {
                fflush(stdout);
                fflush(stderr);
        }
        /* signal EOF to pager */
        close(1);
        close(2);
        if (in_signal)
                finish_command_in_signal(&pager_process);
        else
                finish_command(&pager_process);
}

static void wait_for_pager_atexit(void)
{
        wait_for_pager(0);
}

static void wait_for_pager_signal(int signo)
{
        wait_for_pager(1);
        sigchain_pop(signo);
        raise(signo);
}

static int core_pager_config(const char *var, const char *value, void *data)
{
        if (!strcmp(var, "core.pager"))
                return git_config_string(&pager_program, var, value);
        return 0;
}

const char *git_pager(int stdout_is_tty)
{
        const char *pager;

        if (!stdout_is_tty)
                return NULL;

        pager = getenv("GIT_PAGER");
        if (!pager) {
                if (!pager_program)
                        read_early_config(core_pager_config, NULL);
                pager = pager_program;
        }
        if (!pager)
                pager = getenv("PAGER");
        if (!pager)
                pager = DEFAULT_PAGER;
        if (!*pager || !strcmp(pager, "cat"))
                pager = NULL;

        return pager;
}

static void setup_pager_env(struct argv_array *env)
{
        const char **argv;
        int i;
        char *pager_env = xstrdup(PAGER_ENV);
        int n = split_cmdline(pager_env, &argv);

        if (n < 0)
                die("malformed build-time PAGER_ENV: %s",
                        split_cmdline_strerror(n));

        for (i = 0; i < n; i++) {
                char *cp = strchr(argv[i], '=');

                if (!cp)
                        die("malformed build-time PAGER_ENV");

                *cp = '\0';
                if (!getenv(argv[i])) {
                        *cp = '=';
                        argv_array_push(env, argv[i]);
                }
        }
        free(pager_env);
        free(argv);
}

void prepare_pager_args(struct child_process *pager_process, const char *pager)
{
        argv_array_push(&pager_process->args, pager);
        pager_process->use_shell = 1;
        setup_pager_env(&pager_process->env_array);
}

void setup_pager(void)
{
        const char *pager = git_pager(isatty(1));

        if (!pager)
                return;

        /*
         * force computing the width of the terminal before we redirect
         * the standard output to the pager.
         */
        (void) term_columns();

        setenv("GIT_PAGER_IN_USE", "true", 1);

        /* spawn the pager */
        prepare_pager_args(&pager_process, pager);
        pager_process.in = -1;
        argv_array_push(&pager_process.env_array, "GIT_PAGER_IN_USE");
        if (start_command(&pager_process))
                return;

        /* original process continues, but writes to the pipe */
        dup2(pager_process.in, 1);
        if (isatty(2))
                dup2(pager_process.in, 2);
        close(pager_process.in);

        /* this makes sure that the parent terminates after the pager */
        sigchain_push_common(wait_for_pager_signal);
        atexit(wait_for_pager_atexit);
}

int pager_in_use(void)
{
        const char *env;
        env = getenv("GIT_PAGER_IN_USE");
        return env ? git_config_bool("GIT_PAGER_IN_USE", env) : 0;
}

/*
 * Return cached value (if set) or $COLUMNS environment variable (if
 * set and positive) or ioctl(1, TIOCGWINSZ).ws_col (if positive),
 * and default to 80 if all else fails.
 */
int term_columns(void)
{
        static int term_columns_at_startup;

        char *col_string;
        int n_cols;

        if (term_columns_at_startup)
                return term_columns_at_startup;

        term_columns_at_startup = 80;

        col_string = getenv("COLUMNS");
        if (col_string && (n_cols = atoi(col_string)) > 0)
                term_columns_at_startup = n_cols;
#ifdef TIOCGWINSZ
        else {
                struct winsize ws;
                if (!ioctl(1, TIOCGWINSZ, &ws) && ws.ws_col)
                        term_columns_at_startup = ws.ws_col;
        }
#endif

        return term_columns_at_startup;
}

/*
 * How many columns do we need to show this number in decimal?
 */
int decimal_width(uintmax_t number)
{
        int width;

        for (width = 1; number >= 10; width++)
                number /= 10;
        return width;
}

struct pager_command_config_data {
        const char *cmd;
        int want;
        char *value;
};

static int pager_command_config(const char *var, const char *value, void *vdata)
{
        struct pager_command_config_data *data = vdata;
        const char *cmd;

        if (skip_prefix(var, "pager.", &cmd) && !strcmp(cmd, data->cmd)) {
                int b = git_config_maybe_bool(var, value);
                if (b >= 0)
                        data->want = b;
                else {
                        data->want = 1;
                        data->value = xstrdup(value);
                }
        }

        return 0;
}

/* returns 0 for "no pager", 1 for "use pager", and -1 for "not specified" */
int check_pager_config(const char *cmd)
{
        struct pager_command_config_data data;

        data.cmd = cmd;
        data.want = -1;
        data.value = NULL;

        read_early_config(pager_command_config, &data);

        if (data.value)
                pager_program = data.value;
        return data.want;
}