package git

import (
	"fmt"
	"strings"

	"github.com/bluekeyes/go-gitdiff/gitdiff"
	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/object"
)

type TextFragment struct {
	Header      string
	Lines       []gitdiff.Line
	OldPosition int64
	NewPosition int64
}

type Diff struct {
	Name struct {
		Old string
		New string
	}
	TextFragments []TextFragment
	IsBinary      bool
	IsNew         bool
	IsDelete      bool
	IsRename      bool
}

type NiceDiff struct {
	Diff    []Diff
	Commit  *Commit
	Parents []string // list of short hashes
	Stat    struct {
		FilesChanged int
		Insertions   int
		Deletions    int
	}
}

func (g *Repo) Diff() (*NiceDiff, error) {
	c, err := g.r.CommitObject(g.h)
	if err != nil {
		return nil, fmt.Errorf("commit object: %w", err)
	}

	patch, parents, err := g.getPatch(c)
	if err != nil {
		return nil, err
	}

	nd, err := parseNiceDiff(patch.String())
	if err != nil {
		return nil, err
	}
	nd.Commit = newCommit(c)
	nd.Parents = parents
	return nd, nil
}

func parseNiceDiff(patch string) (*NiceDiff, error) {
	nd := &NiceDiff{}
	if strings.TrimSpace(patch) == "" {
		return nd, nil
	}

	diffs, _, err := gitdiff.Parse(strings.NewReader(patch))
	if err != nil {
		return nil, fmt.Errorf("parsing diff: %w", err)
	}

	nd.Stat.FilesChanged = len(diffs)
	nd.Diff = make([]Diff, len(diffs))
	for i, d := range diffs {
		diff := &nd.Diff[i]
		diff.Name.New = d.NewName
		if d.OldName != d.NewName {
			diff.Name.Old = d.OldName
		}
		diff.IsBinary = d.IsBinary
		diff.IsNew = d.IsNew
		diff.IsDelete = d.IsDelete
		diff.IsRename = d.IsRename

		for _, tf := range d.TextFragments {
			diff.TextFragments = append(diff.TextFragments, TextFragment{
				Header:      tf.Header(),
				Lines:       tf.Lines,
				OldPosition: tf.OldPosition,
				NewPosition: tf.NewPosition,
			})
			for _, l := range tf.Lines {
				switch l.Op {
				case gitdiff.OpAdd:
					nd.Stat.Insertions += 1
				case gitdiff.OpDelete:
					nd.Stat.Deletions += 1
				}
			}
		}
	}
	return nd, nil
}

func (g *Repo) getPatch(c *object.Commit) (*object.Patch, []string, error) {
	commitTree, err := c.Tree()
	if err != nil {
		return nil, nil, err
	}

	parentTree := &object.Tree{}
	if c.NumParents() > 0 {
		parent, perr := c.Parents().Next()
		if perr != nil {
			return nil, nil, perr
		}
		if parentTree, err = parent.Tree(); err != nil {
			return nil, nil, err
		}
	}

	patch, err := parentTree.Patch(commitTree)
	if err != nil {
		return nil, nil, fmt.Errorf("patch: %w", err)
	}

	parents := make([]string, len(c.ParentHashes))
	for i, h := range c.ParentHashes {
		parents[i] = newShortHash(h)
	}

	return patch, parents, nil
}

func (g *Repo) diffBetween(base, head plumbing.Hash) (*NiceDiff, error) {
	baseCommit, err := g.r.CommitObject(base)
	if err != nil {
		return nil, fmt.Errorf("base commit object %s: %w", base, err)
	}
	headCommit, err := g.r.CommitObject(head)
	if err != nil {
		return nil, fmt.Errorf("head commit object %s: %w", head, err)
	}

	baseTree, err := baseCommit.Tree()
	if err != nil {
		return nil, fmt.Errorf("base tree %s: %w", base, err)
	}
	headTree, err := headCommit.Tree()
	if err != nil {
		return nil, fmt.Errorf("head tree %s: %w", head, err)
	}

	patch, err := baseTree.Patch(headTree)
	if err != nil {
		return nil, fmt.Errorf("tree patch %s..%s: %w", base, head, err)
	}

	diff, err := parseNiceDiff(patch.String())
	if err != nil {
		return nil, fmt.Errorf("parse tree diff %s..%s: %w", base, head, err)
	}
	return diff, nil
}