package gitcmd

import (
	"errors"
	"fmt"
	"os/exec"
	"strings"
)

type MergeResult struct {
	Base        string   `json:"base"`
	Head        string   `json:"head"`
	MergeCommit *Commit  `json:"merge_commit,omitempty"`
	FastForward bool     `json:"fast_forward"`
	Conflicts   []string `json:"conflicts,omitempty"`
}

func (r *Repository) Merge(base, head, message, authorName, authorEmail string, noFF bool) (*MergeResult, error) {
	baseSHA, err := r.refSHA("refs/heads/" + base)
	if err != nil || baseSHA == "" {
		return nil, fmt.Errorf("base branch %q not found", base)
	}
	headSHA, err := r.refSHA("refs/heads/" + head)
	if err != nil || headSHA == "" {
		return nil, fmt.Errorf("head branch %q not found", head)
	}

	if !noFF && r.isAncestor(baseSHA, headSHA) {
		if err := r.updateRef("refs/heads/"+base, headSHA, baseSHA); err != nil {
			return nil, err
		}
		hc, err := r.GetCommit(headSHA)
		if err != nil {
			return nil, err
		}
		return &MergeResult{Base: base, Head: head, MergeCommit: hc, FastForward: true}, nil
	}

	out, _, err := NewCommand("merge-tree", "--write-tree", "-z", "--name-only", "--no-messages").
		AddDynamicArguments(baseSHA, headSHA).
		WithDir(r.Path).RunStdString(r.ctx)

	conflict := false
	if err != nil {
		var exitErr *exec.ExitError
		if errors.As(err, &exitErr) && exitErr.ExitCode() == 1 {
			conflict = true
		} else {
			return nil, fmt.Errorf("merge-tree: %w", err)
		}
	}

	parts := strings.Split(out, "\x00")
	if len(parts) == 0 || strings.TrimSpace(parts[0]) == "" {
		return nil, fmt.Errorf("merge-tree: empty output")
	}
	mergedTree := strings.TrimSpace(parts[0])

	if conflict {
		var conflicts []string
		for i := 1; i < len(parts); i++ {
			if p := strings.TrimSpace(parts[i]); p != "" {
				conflicts = append(conflicts, p)
			}
		}
		return &MergeResult{Base: base, Head: head, Conflicts: conflicts}, nil
	}

	commitSHA, err := r.commitTree(mergedTree, message, authorName, authorEmail, r.Path, baseSHA, headSHA)
	if err != nil {
		return nil, err
	}
	if err := r.updateRef("refs/heads/"+base, commitSHA, baseSHA); err != nil {
		return nil, err
	}
	mc, err := r.GetCommit(commitSHA)
	if err != nil {
		return nil, err
	}
	return &MergeResult{Base: base, Head: head, MergeCommit: mc}, nil
}