// SPDX-License-Identifier: GPL-2.0
#include <sys/select.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <sys/ioctl.h>
#include "pager.h"
#include "run-command.h"
#include "sigchain.h"
#include "subcmd-config.h"

/*
 * This is split up from the rest of git so that we can do
 * something different on Windows.
 */

static int spawned_pager;
static int pager_columns;

void pager_init(const char *pager_env)
{
        subcmd_config.pager_env = pager_env;
}

static const char *forced_pager;

void force_pager(const char *pager)
{
        forced_pager = pager;
}

static void pager_preexec(void)
{
        /*
         * Work around bug in "less" by not starting it until we
         * have real input
         */
        fd_set in;
        fd_set exception;

        FD_ZERO(&in);
        FD_ZERO(&exception);
        FD_SET(0, &in);
        FD_SET(0, &exception);
        select(1, &in, NULL, &exception, NULL);

        setenv("LESS", "FRSX", 0);
}

static const char *pager_argv[] = { "sh", "-c", NULL, NULL };
static struct child_process pager_process;

static void wait_for_pager(void)
{
        fflush(stdout);
        fflush(stderr);
        /* signal EOF to pager */
        close(1);
        close(2);
        finish_command(&pager_process);
}

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

void setup_pager(void)
{
        const char *pager = getenv(subcmd_config.pager_env);
        struct winsize sz;

        if (forced_pager)
                pager = forced_pager;
        if (!isatty(1) && !forced_pager)
                return;
        if (ioctl(1, TIOCGWINSZ, &sz) == 0)
                pager_columns = sz.ws_col;
        if (!pager)
                pager = getenv("PAGER");
        if (!(pager || access("/usr/bin/pager", X_OK)))
                pager = "/usr/bin/pager";
        if (!(pager || access("/usr/bin/less", X_OK)))
                pager = "/usr/bin/less";
        if (!pager)
                pager = "cat";
        if (!*pager || !strcmp(pager, "cat"))
                return;

        spawned_pager = 1; /* means we are emitting to terminal */

        /* spawn the pager */
        pager_argv[2] = pager;
        pager_process.argv = pager_argv;
        pager_process.in = -1;
        pager_process.preexec_cb = pager_preexec;

        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);
}

int pager_in_use(void)
{
        return spawned_pager;
}

int pager_get_columns(void)
{
        char *s;

        s = getenv("COLUMNS");
        if (s)
                return atoi(s);

        return (pager_columns ? pager_columns : 80) - 2;
}